Test-retest measurements of dopamine D1-type receptors using simultaneous PET/MRI imaging.

PURPOSE: The role of dopamine D1-type receptor (D1R)-expressing neurons in the regulation of motivated behavior and reward prediction has not yet been fully established. As a prerequisite for future research assessing D1-mediated neuronal network regulation using simultaneous PET/MRI and D1R-selective [11C]SCH23390, this study investigated the stability of central D1R measurements between two independent PET/MRI sessions under baseline conditions. METHODS: Thirteen healthy volunteers (7 female, age 33 ± 13 yrs) underwent 90-min emission scans, each after 90-s bolus injection of 486 ± 16 MBq [11C]SCH23390, on two separate days within 2-4 weeks using a PET/MRI system. Parametric images of D1R distribution volume ratio (DVR) and binding potential (BPND) were generated by a multi-linear reference tissue model with two parameters and the cerebellar cortex as receptor-free reference region. Volume-of-interest (VOI) analysis was performed with manual VOIs drawn on consecutive transverse MRI slices for brain regions with high and low D1R density. RESULTS: The DVR varied from 2.5 ± 0.3 to 2.9 ± 0.5 in regions with high D1R density (e.g. the head of the caudate) and from 1.2 ± 0.1 to 1.6 ± 0.2 in regions with low D1R density (e.g. the prefrontal cortex). The absolute variability of the DVR ranged from 2.4% ± 1.3% to 5.1% ± 5.3%, while Bland-Altman analyses revealed very low differences in mean DVR (e.g. 0.013 ± 0.17 for the nucleus accumbens). Intraclass correlation (one-way, random) indicated very high agreement (0.93 in average) for both DVR and BPND values. Accordingly, the absolute variability of BPND ranged from 7.0% ± 4.7% to 12.5% ± 10.6%; however, there were regions with very low D1R content, such as the occipital cortex, with higher mean variability. CONCLUSION: The test-retest reliability of D1R measurements in this study was very high. This was the case not only for D1R-rich brain areas, but also for regions with low D1R density. These results will provide a solid base for future joint PET/MRI data analyses in stimulation-dependent mapping of D1R-containing neurons and their effects on projections in neuronal circuits that determine behavior.

Dissonance in Music Impairs Spatial Gait Parameters in Patients with Parkinson's Disease.

BACKGROUND: It is known that music influences gait parameters in Parkinson's disease (PD). However, it remains unclear whether this effect is merely due to temporal aspects of music (rhythm and tempo) or other musical parameters. OBJECTIVE: To examine the influence of pleasant and unpleasant music on spatiotemporal gait parameters in PD, while controlling for rhythmic aspects of the musical signal. METHODS: We measured spatiotemporal gait parameters of 18 patients suffering from mild PD (50%men, mean±SD age of 64±6 years; mean disease duration of 6±5 years; mean Unified PD Rating scale [UPDRS] motor score of 15±7) who listened to eight different pieces of music. Music pieces varied in harmonic consonance/dissonance to create the experience of pleasant/unpleasant feelings. To measure gait parameters, we used an established analysis of spatiotemporal gait, which consists of a walkway containing pressure-receptive sensors (GAITRite®). Repeated measures analyses of variance were used to evaluate effects of auditory stimuli. In addition, linear regression was used to evaluate effects of valence on gait. RESULTS: Sensory dissonance modulated spatiotemporal and spatial gait parameters, namely velocity and stride length, while temporal gait parameters (cadence, swing duration) were not affected. In contrast, valence in music as perceived by patients was not associated with gait parameters. Motor and musical abilities did not relevantly influence the modulation of gait by auditory stimuli. CONCLUSION: Our observations suggest that dissonant music negatively affects particularly spatial gait parameters in PD by yet unknown mechanisms, but putatively through increased cognitive interference reducing attention in auditory cueing.

Musical Agency during Physical Exercise Decreases Pain.

Objectives: When physical exercise is systematically coupled to music production, exercisers experience improvements in mood, reductions in perceived effort, and enhanced muscular efficiency. The physiology underlying these positive effects remains unknown. Here we approached the investigation of how such musical agency may stimulate the release of endogenous opioids indirectly with a pain threshold paradigm. Design: In a cross-over design we tested the opioid-hypothesis with an indirect measure, comparing the pain tolerance of 22 participants following exercise with or without musical agency. Method: Physical exercise was coupled to music by integrating weight-training machines with sensors that control music-synthesis in real time. Pain tolerance was measured as withdrawal time in a cold pressor test. Results: On average, participants tolerated cold pain for ~5 s longer following exercise sessions with musical agency. Musical agency explained 25% of the variance in cold pressor test withdrawal times after factoring out individual differences in general pain sensitivity. Conclusions: This result demonstrates a substantial pain reducing effect of musical agency in combination with physical exercise, probably due to stimulation of endogenous opioid mechanisms. This has implications for exercise endurance, both in sports and a multitude of rehabilitative therapies in which physical exercise is effective but painful.

The Band Effect-Physically Strenuous Music Making Increases Esthetic Appreciation of Music.

The esthetic appreciation of music is strongly influenced by cultural background and personal taste. One would expect that this would complicate the utilizability of musical feedback in paradigms, such that music would only be perceived as a reward if it complies to personal esthetic appreciation. Here we report data where we assessed esthetic appreciation of music after 1. a physically strenuous music improvisation and 2. after passive music listening (where participants esthetically assessed similar music). Data are reported from two experiments with different patient groups: 1. Drug abuse patients, and 2. Chronic pain patients. Participants in both experiments performed Jymmin, a music feedback method where exercise equipment is modified in such a way that it can be played like musical instruments by modulating musical parameters in a composition software. This combines physical exertion with musical performance in a fashion that has previously been shown to have a number of positive psychological effects such as enhanced mood and reduced perceived exertion. In both experiments esthetic appreciation of musical presentations during Jymmin and a control condition without musical agency were compared. Data show that both patient groups perceived the musical outcome of their own performance as more esthetically pleasing than similar music they listened to passively. This suggests that the act of making music (when combined with physical exertion) is associated with a positivity bias about the perceived esthetical quality of the musical outcome. The outcome of personal musical agency thus tends to be perceived as rewarding even if it does not comply with personal esthetic appreciation. This suggests that musical feedback interventions may not always have to be highly individualized because individual taste may not always be crucial. The results also suggest that the method applied here may be efficient at encouraging music listeners to actively explore new musical styles that they might otherwise be reluctant to listen to (e.g., avant-garde music). The results also hint toward a deeper understanding of why musicians, who exert themselves physically during musical performances to generate music and regardless of the type of music they are playing, typically find the physically demanding experience esthetically satisfying.

Losing track of time through delayed body representations.

The ability to keep track of time is perceived as crucial in most human societies. However, to lose track of time may also serve an important social role, associated with recreational purpose. To this end a number of social technologies are employed, some of which may relate to a manipulation of time perception through a modulation of body representation. Here, we investigated an influence of real-time or delayed videos of own-body representations on time perception in an experimental setup with virtual mirrors. Seventy participants were asked to either stay in the installation until they thought that a defined time (90 s) had passed, or they were encouraged to stay in the installation as long as they wanted and after exiting were asked to estimate the duration of their stay. Results show that a modulation of body representation by time-delayed representations of the mirror-video displays influenced time perception. Furthermore, these time-delayed conditions were associated with a greater sense of arousal and intoxication. We suggest that feeding in references to the immediate past into working memory could be the underlying mental mechanism mediating the observed modulation of time perception. We argue that such an influence on time perception would probably not only be achieved visually, but might also work with acoustic references to the immediate past (e.g., with music).

Musical feedback during exercise machine workout enhances mood.

Music making has a number of beneficial effects for motor tasks compared to passive music listening. Given that recent research suggests that high energy musical activities elevate positive affect more strongly than low energy musical activities, we here investigated a recent method that combined music making with systematically increasing physiological arousal by exercise machine workout. We compared mood and anxiety after two exercise conditions on non-cyclical exercise machines, one with passive music listening and the other with musical feedback (where participants could make music with the exercise machines). The results showed that agency during exercise machine workout (an activity we previously labeled jymmin - a cross between jammin and gym) had an enhancing effect on mood compared to workout with passive music listening. Furthermore, the order in which the conditions were presented mediated the effect of musical agency for this subscale when participants first listened passively, the difference in mood between the two conditions was greater, suggesting that a stronger increase in hormone levels (e.g., endorphins) during the active condition may have caused the observed effect. Given an enhanced mood after training with musical feedback compared to passively listening to the same type of music during workout, the results suggest that exercise machine workout with musical feedback (jymmin) makes the act of exercise machine training more desirable.